1. Technical Field
This invention relates generally to antenna structures for portable electronic devices, and more particularly to an inverted antenna structure for a mobile device having selectably one of a uniform antenna coverage pattern and a uniformly azimuthal antenna coverage pattern in the upper hemisphere.
2. Background Art
Portable electronic devices, like mobile telephones for example, employ one or more antennas for transmission and reception of radio frequency (RF) signals to and from other devices and network base stations. These antennas each have a characteristic “antenna pattern” that describes from which directions the antennas are best suited to transmit and receive signals. For optimal performance, these antenna patterns should be shaped such that they extend outward towards the devices with which they communicate. For devices like mobile telephones, the antenna patterns should generally be directed outward from a user, as the towers to which the mobile telephone sends and receives signals are generally a few hundred feet off the ground.
In certain applications however, like mobile devices that receive signals from satellites orbiting the earth, the traditional cellular antenna patterns are not optimal. For instance, devices that include Global Positioning Systems (GPS) require different antenna patterns to reliably receive signals from satellites. When such a device is outdoors, the satellites, of course, are orbiting overhead. As such, an optimal antenna pattern should extend predominantly upwards and should be substantially uniform. When the device is indoors, however, satellite signals generally enter through the windows. The outdoor pattern, i.e. a pattern pointing upward and substantially uniform, may not be optimum for signals entering through windows. A different indoor pattern, suitable for receiving signals that enter buildings through windows, is required.
Prior art mobile telephone antenna structures often fail to provide adequate uniformity to reliably receive satellite signals both indoors and out. For instance, traditional mobile telephones that have either retractable or stub antennas extending from a portion of the telephone tend to have antenna patterns that do not change. In other words, the antenna pattern is the same indoors as out. Further, devices that include additional antenna structures in an attempt to be satellite compatible may have upward pointing antenna patterns, but they are rarely uniform. This is especially true when the device is being held next to the body of a user.
There is thus a need for an improved antenna structure having a substantially upward pointing, uniform antenna pattern so as to be compatible with satellite signal reception.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.